A conventional ball chair is shown in FIGS. 6 and 7. The conventional ball chair is disadvantageous because it may be unstable when the user is sitting thereon and the ball may even fall off the chair, which can cause accident or injury to the user. Thus, the conventional ball chair has been modified to increase the stability of the ball. The modified ball chair may have a connecting portion 32 on top of the through hole 31 of the chair base 30 and a positioning unit 33 is disposed on the connecting portion 32 to further restrict the ball 34 to prevent the ball from falling off.
However, conventional ball chair described above still has some problems: the connecting portion 32 has a plurality of through holes and the positioning unit 33 has a screw 331 corresponding to the connecting portion 32 and is inserted to the connecting portion 32 to engage with a nut 332. Although the positioning unit 33 can be secured on the connecting portion 32, it is difficult for the user to assemble the ball chair. Furthermore, the ball 34 may be damaged by the screw 331.
Moreover, referring to FIG. 8 for another conventional ball chair 40, which has a positioning unit 41 and the positioning unit 41 cannot be removed from the ball chair 40, so the size of the ball chair increases, which may increase the costs for transportation and increase the usage of the packaging materials.
Therefore, there remains a need for a new and improved design for a ball chair to overcome the problems presented above.